1. Field of the Invention
The invention relates to data links and, more particularly, to high speed data links for rotating displays.
2. Prior Art
Data links carry information between spatially separated points. As society's ability to generate and process data increases, the need for data links which can transmit large volumes of data at high speeds in diverse environments has increased concomitantly.
One field of technology in which the need for reliable, high speed, high volume data links has become critical is the field of rotating displays. An example of such a display is described in U.S. Pat. No. 4,160,973 issued July 10, 1979 to Edward P. Berlin, Jr., and entitled "Three-Dimensional Display." The invention described therein comprises a two-dimensional planar display formed from a matrix arrangement of light emitting diodes and rotated about a central axis to sweep out a three dimensional volume in which the physiological effects of vision persistence are used to provide the appearance of a true three-dimensional display. The system described therein provides for the display of in excess of four million "points" or pixels, each of which can be displayed in any one of 16 intensity levels using a four-bit gray scale. Accordingly, an excess of 16 million bits of information are required for the display. If each element is to be changeable at a rate which is comparable to the frame rate of television raster displays so as to reduce "flicker" of the display, a data rate of nearly 500 million bits per second is called for. This imposes extraordinary demands on the data communications link between the rotating display and the stationary data source.
Heretofore it has been proposed to use an optical data link, specifically, one or more photodiode transmitters mounted on the stationary data source and a corresponding number of phototransistor receivers mounted on the rotating display, the photodiodes and the corresponding phototransistors being mechanically and electrically separated from each other and being coupled only via an optical path. This type of data link, while particularly suited for this application, nonetheless possesses several disadvantages. To begin with, the data rate that can be transmitted over a single photodiode-phototransistor pair is limited, and a number of such coupling elements operating in parallel may be required to transmit data reliably at the rates called for by this type of display. However, when more than a single photodiode-phototransistor pair is utilized, the additional elements must be placed off-axis and coupling between the stationary source and the moving display becomes a severe problem. Further, it is critically important that dust or other environmental contamination be excluded from the operating environment, since this can introduce errors in the data transmission. This is particularly a problem at the high data rates called for by such a display.